Shellfish is a term used by cooks which includes crustaceans such as shrimps, crawfish, crabs, lobster, langoustines, and
mollusks such as clam, mussels oysters, scallops, and sea urchins.
Shellfish allergy is one of the most common food allergies in the United States, affecting about 2% of the adult population. It is not
very common in children. In the United States, the highest rate of shellfish allergy occurs in African American adults. Overall,
shellfish allergy accounts for up to 1/3 of all serious allergic reactions. Shellfish allergy is usually lifelong- it rarely goes away.
Different people will have different sensitivities to shellfish, so that some may react to trace amounts found in the air from the food
being cooked, while others won’t have a reaction until a few bite size pieces have been swallowed.
Typically, individuals allergic to 1 type of shellfish have a very high chance (75%) of becoming allergic to other shellfish. It is thus
very important to avoid all shellfish types, not just the one or two that you might initially have had a problem with.
There is little, if any, cross-reactivity between fish and shellfish. Studies demonstrate that only about 10% of people allergic to
shellfish will also have a problem with fish (and vice versa). Caution must be taken when eating fish however, as shellfish is
often processed on the same equipment used to process fish, leading to possible contamination of the fish with shellfish particles.
Are Shellfish Allergic Individuals Allergic to Iodine?
This is a common misconception. The idea that shellfish allergic patients could have problems with iodine appears to have
started in the 1970’s and has been widely disseminated ever since. However, there is no evidence that this is true. There is no
relationship between shellfish, iodine, and radio contrast dyes.
- Shellfish allergic individuals do not have an increased risk of adverse reactions when eating foods containing iodine (an
element found in almost everything we eat).
- Shellfish allergic individuals have no increased risk of a reaction from antiseptics such as Betadine (10% povidone with
Iodine solution, often before surgical procedures to clean the skin) compared to non-shellfish allergic people.
- While allergies to radiological dyes do exist, the risk of a reaction in patients with a shellfish allergy is no greater than
someone who is not shellfish allergic.
Avoiding shellfish may appear easy at first glance, but accidental exposures occur frequently. It is not uncommon for people to
have reactions in restaurants where the person had their meal prepared in a pan that was previously used to cook some type of
shellfish. It is thus important to request that your meal be prepared on cookware that has been cleaned so that there are no
residual amounts of shellfish from a previous meal in your food. It is also important to read labels carefully, as shellfish can
sometimes be added as a flavoring in foods you might not otherwise be expected to contain this type of food. Reading labels of
over the counter products, including “natural” remedies and herbal supplements is also important. For example, some weight loss
products contain small amounts of a shellfish derivative called Chitosan. Glucosamine, commonly used in over the counter
products for osteoarthritis, can also be derived from the shells of crabs and lobsters. While there is no conclusive evidence that
Chitosan and Glucosamine are harmful in patients who are allergic to shellfish, it is best to avoid these products until further
discussion with your allergist who can do some tests to ensure they are safe for you to ingest.
Avoid foods that contain:
- Sea urchin
Foods that may contain shellfish:
- Fish stock
Make sure to check out the coping with food allergies page for school and traveling tips, and useful links including sites that sell
allergy safe foods, medic alert bracelets. There's even a link to a website that will translate food allergy words in just about any
language you can imagine!